The present invention relates to an automatic automobile headlamp leveling device for automatically adjusting the tilt of headlamps of a vehicle based on a tilt of the vehicle in a longitudinal direction thereof (hereinafter, referred to as a pitch angle) in a direction in which the light axes of the headlamps are adjusted so as to offset the tilt of the vehicle (hereinafter, referred to as automatic leveling).
A headlamp of this kind is constructed, for instance, such that a reflector having a light source securely inserted thereinto is supported in such a manner as to be tilted about a horizontal tilting shaft relative to a lamp body and that the light axis of the reflector (headlamp) is tilted by an actuator about the horizontal tilting shaft.
A conventional automatic headlamp leveling device comprises a pitch angle detection means, a vehicle speed sensor and a control section for controlling the driving of actuators based on detection signals from the detection means and sensor, which are mounted on a vehicle for adjusting light axes of the headlamps (reflectors) of the vehicle such that the light axes stay in a certain state relative to the surface of a road at all times.
The conventional automatic headlamp leveling device is, however, constructed such that the leveling of headlamps of a vehicle is performed in real time, whether the vehicle is moving or not, in response to changes in vehicle posture, resulting when the vehicle is accelerated or decelerated while running, or changes in load, resulting from luggage being loaded and unloaded, or when occupants get in or out of the vehicle. Due to the frequency of these potential changes, the number of times when the actuator is activated is highly increased, power consumption is increased, and a high durability is required for driving mechanism constituent components such as motors, gears and the like. All of these factors result in high productions costs.
To cope with this problem, an automatic headlamp leveling device (JP-A-10-264221) was proposed with a view to providing an automatic headlamp leveling device that is inexpensive and which has a long service life by reducing the frequency at which the actuators are driven. The proposed automatic headlamp leveling device being constructed such that the driving of actuators is controlled at certain intervals while the vehicle is stopped. While the vehicle is running, the driving of the actuators is controlled only once, provided the vehicle is running in a stable fashion in which certain speed and acceleration continues for a predetermined length of time.
A drawback with the proposed automatic headlamp leveling device is that the vehicle height sensor, which is the pitch angle detection means, may detect a change in pitch angle when the vehicle is turning or slaloming, and the control section judges such a state as a stable running, whereby appropriate automatic headlamp leveling cannot be carried out. This problem will be described below referring to FIGS. 7 and 8 showing output characteristics of vehicle speeds and vehicle postures after the vehicle starts to run. FIG. 7 shows a case in which the vehicle turns while running at a constant speed, and FIG. 8 shows a case in which the vehicle slaloms while running at a constant speed.
FIG. 7, is a case where the vehicle height sensor, acting as the pitch angle detection means, is mounted on, for instance, the rear right-hand side of the vehicle suspension. Here, when the vehicle turns left while running at a constant speed, the right-hand side of the suspension dives (contracts) due to an acceleration of gravity when turning, and the vehicle height sensor, mounted on the suspension, detects this dive as a tilt of the vehicle in a longitudinal direction thereof (i.e., a change in pitch angle of the vehicle) (refer to a characteristic Axe2x80x2 in FIG. 7). Due to this, the automatic headlamp leveling device (the control section) judges that stable running conditions are met if the pitch angle data xcex8, detected by the vehicle height sensor, continues for a predetermined length of time (refer to reference character t1 in FIG. 7), and performs a leveling (controlling) of the light axes of the headlamps in a downward direction. This reduces a visible distance in front of the vehicle, which is undesirable from the safe driving point of view.
On the contrary, when the vehicle turns right, the vehicle height sensor mounted on the rear left-hand side suspension floats (extends), as shown by a characteristic Bxe2x80x2 in FIG. 7. If this state continues for a predetermined length of time, the automatic headlamp leveling device (the control section) performs a leveling (controlling) of the light axes of the headlamps in an upward direction. This generates glaring light, which is undesirable to an oncoming vehicle.
In addition, when the vehicle slaloms, as shown in FIG. 8, the rear left-hand side suspension on which the vehicle height sensor is mounted dives and floats (contracts and extends). In such a vehicle running state, the vehicle height sensor also detects tilts in the longitudinal direction of the vehicle (changes in pitch angle), and if this state continues over the predetermined length of time, the automatic headlamp leveling device (the control section) performs erroneous light axes leveling, which is also undesirable.
The present invention was made in view of the aforesaid problems inherent in the prior art, and an object thereof is to provide an automatic automobile headlamp leveling device that is inexpensive and which has a long service life by reducing the frequency at which actuators are driven to thereby improve the improper automatic headlamp leveling when a vehicle is running.
With a view to attaining the aforesaid object, a first embodiment of the invention provides an automatic automobile headlamp leveling device comprising headlamps adapted to be driven by an actuator such that a light axis thereof is tilted up and/or down relative to a vehicle body, control means for controlling the driving of the actuators, vehicle speed detection means for detecting the speed of a vehicle, pitch angle detection means for detecting a pitch angle of the vehicle, and a storage section for storing pitch angle data of the vehicle detected by the pitch angle detection means, the control means controlling the driving of the actuators based on pitch angle data detected by the pitch angle detection means such that the light axes of the headlamps always stay in a certain tilted state relative to the surface of a road, wherein the control means judges whether the vehicle is at a stop or is running based on outputs from the vehicle speed sensors and then controls the driving of the actuators at certain intervals when the vehicle is at a stop, and while the vehicle is running, it controls the driving of said actuators only once during a stable running. The automatic automobile headlamp leveling device being characterized in that the control means judges as an inappropriate leveling state a state in which a pitch angle is continuously detected while the vehicle is running which differs from pitch angle data taken when the vehicle is at a stop by a predetermined value or greater and then stops controlling the driving of the actuators.
The inappropriate leveling states are referred to, respectively, as a vehicle turning state, in which pitch angle data is greater (or smaller), by a predetermined value, than pitch angle data taken when the vehicle is at a stop, is detected continuously for a predetermined length of time or longer, and a vehicle slaloming state, in which pitch angle data is greater and smaller, by a predetermined value, than pitch angle data taken when the vehicle is at a stop is detected alternately.
In this invention, it is premised that the leveling (light axis correction) is carried out based on pitch angle data taken when the vehicle is at a stop. Pitch angle data taken when the vehicle is at a stop is more accurate than when taken as the vehicle is running to the extent that the former is affected by disturbance factors less than the later. Since the driving of the actuators is controlled based on the accurate pitch angle data, a more accurate automatic headlamp leveling becomes possible.
In addition, since the controlling of the driving of the actuators when the vehicle is at a stop is so limited that they are controlled every time a predetermined length of time elapses, the frequency at which the actuators are activated is reduced, whereby power can be saved and the wear of the driving mechanism constituent members is limited.
Furthermore, the leveling (light axis correction) based on pitch angle data when the vehicle is running corrects the result of a leveling carried out based on pitch angle data taken when the vehicle is at a stop in an inappropriate condition such as one where the vehicle is parked on an inclined road or the vehicle is parked on a curb.
Moreover, the control means judges on an inappropriate leveling state (a turning state and a slaloming state) that is easily taken for a stable running state based on pitch angle data detected while the vehicle is running and stops a leveling during such an inappropriate leveling state, and therefore erroneous automatic headlamp leveling can be avoided.
An invention according to a second preferred embodiment provides an automatic automobile headlamp leveling device as described by the first embodiment, wherein the control means controls the driving of the actuators to level the headlamps based on pitch angle data taken when the vehicle is determined to be running in a stable fashion, after the control means had previously made a judgement of an inappropriate leveling state and stopped controlling the driving of the actuators.
Accordingly, when the running state of the vehicle changes from the inappropriate leveling state to the appropriate stable running state, if no control of the driving of the actuators has been carried out while running, the control section controls the driving of the actuators without any delay for appropriate automatic headlamp leveling.
Another embodiment of the invention provides an automatic automobile headlamp leveling device wherein controlling of the actuators is performed only when the headlamps are turned on.
Since the actuators are not activated if no headlamps are turned off, the number of times when the actuators are operated can be reduced, power can be saved, and the wear of the driving mechanism constituent members is limited to such an extent.
Additionally, an automatic automobile headlamp leveling device can be provided wherein the actuator driving intervals are set to be longer than a maximum driving time of the actuator required for each leveling operation.
If an interval between a previous control and a following control is shorter than the maximum driving time of the actuator, the actuator is caused to start the next operation before a target value is reached. This increases the frequency at which the actuator is driven, leading to a reduction of the service life of the actuator. With this construction, however, after is assuredly reaches the target value in the previous control, the actuator is driven to the following control. This reduces the frequency at which the actuator is driven, whereby the service life of the actuator is increased to the extent that the actuator driving frequency is so reduced.
In addition, by extending the interval at which the actuator is driven, a change in pitch angle data within the interval between the previous control to the following control can be omitted without driving the actuator. In other words, every action happening within the interval can be concentrated on the driving of the actuator in the following control, and therefore, the frequency at which the actuator is driven can also be reduced.
Moreover, pitch angle data of the vehicle detected by the pitch angle detection means are at all times taken into the control section for calculation, even during the actuator driving interval. Furthermore, by utilizing all of the pitch angle data taken into the control section as control data, numerous pitch angles can be used as control data, thereby making it possible to perform an appropriate leveling of the headlamps entailed by a detection of accurate vehicle posture (pitch angle).